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“You know, there isn’t a stinker here,” muses St. Antoine while exhaling a gray-blue cloud of cigar smoke.

Our esteemed editor at large is correct in more ways than one. Despite our proximity to the tailpipes of three idling diesels, the dissipating haze of his Partagas Spanish Rosado is replaced by nothing but the cold clean scent of an eastern Sierra winter.

Equally striking is the conspicuous lack of traditional diesel clatter. That’s to be expected of the fourth member of our quartet, the brand-new, eerily quiet 2010 Lexus RX 450h. It is a hybrid after all, but what about the BMW X5 xDrive 35d, Mercedes-Benz ML320 BlueTEC, and Volkswagen Touareg TDI? What does their burbling idle say about the state of modern diesels? Do they stand a chance against the latest hybrid version of the world’s best-selling luxury SUV? We assemble in the mountains to find out.

Our pre-expedition walkaround reveals a few highlights. With an available third-row/seven-passenger configuration, the X5 is the most capacious of all. Though similar in overall length to the Benz and VW, the 107.9-inch wheelbase of the Lexus is shortest by 4.5 inches, a function of its car-based chassis.

Though zee Germans are all powered by 3.0-liter, six-cylinder turbodiesel engines, they differ in the details. BMW sticks by its impressive sequentially twin turbocharged inline-six architecture, while Benz and VW opt for single turbos and vee cylinder arrangements. All three require the latest ultra-low-sulphur diesel fuel and use proprietary variations of AdBlue urea injection to reduce nitrogen-oxide emissions. They run clean, but still can’t touch the Lexus’s SULEV status.

While the Benz retains its comparatively traditional 4-Matic full-time four-wheel-drive system, the X5 serves up Dynamic Traction Control, the rear torque-splitting trickery that puts the “x” in BMW’s xDrive. The Touareg’s 4XMOTION system is the only one to offer full-time four-wheel drive with low range, while the RX 450h again shows its hybrid-car roots. A transversely mounted engine and electric motor/generator power the front wheels, while an additional motor/generator spins the rear wheels on demand.

Our test session’s major surprise isn’t that the X5 trumps all in braking and handling. It’s that the BMW doesn’t sweep the acceleration tests as well. Despite a class-leading 425 pound-feet of torque, the X5 is soundly beaten to 60 mph by the smooth-whirring RX 450h. The whopping 0.3-second disparity seems supported by that tenet of drag-racing mathematics-100 pounds is worth a tenth of a second-but weight can’t be the only issue. Yes, the BMW outweighs the Lexus by just over 300 pounds, but the ML320 weighs 40 pounds less than the X5 and finishes last, 1.7 seconds behind the Lexus. Little mysteries like these swirl in our heads as we trek north on Highway 395.

For all their differences, one thing these lux trucks have in common is the sensory recalibration they require during the first few minutes of driving. Though their sumptuous tuning means neck-snapping launches are kept to a minimum, lead-footing any of the diesels unleashes a veritable tsunami of low-rpm torque.

The X5 elicits the most grins, but not just from its precision-weighted steering and road-hugging dynamics. St. Antoine can’t get enough of its “ocean-liner” torque. “Cruising up the 395 grade out of Bishop, the X5 never even downshifted-just kept grunting away as we stormed up to 8000 feet. Altitude? What altitude?”

The VW impresses for different reasons. “Definitely has a softer suspension and does like to lean in corners, but once used to the motion, taking a set and throttling through corners becomes a blast,” says our colleague and off-road expert Mark Williams. While patters of diesel vibration can be induced from both the Benz and BMW, VW engineers have somehow managed to quash nearly all oil-burning shudders. “Very plush, composed ride, much quieter than the BMW’s,” says senior editor Ron Kiino. Our editors also note the Touareg’s spry response off the line, no mean feat for a beast approaching 5400 pounds. “Almost responds like a V-8 gas engine, without the usual engine lag after you punch the gas,” says Williams.

The oddest bit is how all the diesels feel quicker than the Lexus. “Wait a second, which one was faster at the track?” blurts St. Antoine over the radio, incredulous at how quickly the BMW pulls away from the Lexus on our road loop.

Perhaps a rolling-start advantage? Williams doesn’t think so. “At 7500 feet, these diesels still feel strong and powerful while delivering 20-plus mpg. Not bad for 5000-plus-pound SUVs. The much lighter Lexus with much cooler technology gets hammered in the cold and altitude.”

Yet it’s impossible not to be impressed by the Lexus. Hitting the engine-start button is like pushing the I/O button on the latest quad core PC. Thrums, whirrs, and blinking lights provide the sensation of a complex artificial intelligence booting up.

Light throttle touches send only electrons to the front and rear motor/generators and result in the hush of rolling rubber. Full throttle wakes the 3.5-liter V-6, but you’d never know. With the CVT droning, it’s nearly impossible to pick up exactly when the engine fires up to help things along; there are no additional vibrations and only the slightest auditory cues.

That’s just a taste of the Lexus’s slickly integrated technology. Everywhere you look, the RX 450h is awash in electronic goodies, from the crisp, organic LED display to headlamps that automatically douse their high beams for oncoming traffic to a game-changing telematics controller called Remote Touch. Like a cross between a touch screen and trackball, it allows the user to actually feel the pointer contact icons and virtual buttons. It’s spooky at first, but quick to win converts. “Remote touch does just as its name implies, imparting a rewarding sense of feel and touch as you swirl the ‘mouse’ over the screen. Locks neatly into the various menu buttons, and generally works intuitively,” says St. Antoine. Williams is equally impressed, “If every vehicle gets something like this in 10 years I won’t be surprised.”

In comparison, both the BMW and Benz feel low-tech and spare. The X5’s austere, all-black cabin incites the most complaints: “Somber cockpit and I still hate the iDrive interface, especially when controlling the nav, a deal-breaker in my book,” says Kiino. St. Antoine gently backhands the Benz cabin, “Perhaps not as chic as the VW’s, but this is a nice room, too. Some of the controls work deftly-the climate system, for instance-but others are simply horrible.”

While floored by its low-cost/high-feature set, our judges were split on the Lexus’s overall execution. Some found it a futuristic, techno tour de force, others a modern, yet cheap, mishmash. Williams notes, “Not hot about the exterior design-front nose looks rather unfinished-but the thought and execution of the interior is amazing. Every surface and shape appears sculpted in order to create as much space and visibility as possible. St. Antoine is not so impressed: “Interior is really missing that ‘premium’ feel you expect of a Lexus. The center console feels downright cheap.”

Not so for the Touareg. Kiino likens its cabin to “a den in a ritzy Alaska fishing lodge,” while St. Antoine gushes, “What a gorgeous environment for conducting the business of driving. The Touareg has a very serious feel, yet still manages to look stylish and inviting. See, BMW? It can be done.”

Halfway through our journey back home, Williams calls over the radio, “Guys, the Lexus is showing 36 miles to empty.” Our plan has been to stop nearly 200 miles farther down the road, but we have to pull over, even though all the diesels show half-filled tanks and remaining ranges approaching 300 miles. As the pumps click off gallons and dollars, our head-scratching begins.

To no one’s surprise, the hybrid Lexus bests all in real-world fuel economy. At 23.0 mpg, the RX 450h beats its next closest rival, the surprisingly efficient X5, by 1 mpg. Bringing up the rear is the Touareg, which is 2.5 mpg down on the Lexus. Easy call, then? No, because mpg is only one way of looking at this equation.

Dollars is another, and the difference in fuel costs between the Lexus and the Volkswagen over our 600-mile journey came out to only $10.17. Sound like a lot? Factor in what you get for that extra 10 bucks: 407 pound-feet of torque and the ability to haul over 7700 pounds-more than twice that of the Lexus. Was this a capability we exploited on this trip? No, but it’s certainly food for thought for anyone who expects an SUV to tow a boat or boatloads of gear.

Then there’s the range factor. With only 19.2 gallons onboard, the RX 450h’s fuel sipping strategy is effectively negated when matched up against the diesels’ large tanks. Using the EPA highway numbers, the Touareg could theoretically cover 660 miles on its 26.2-gallon tank. Our real-world mileage ended up significantly lower, but our calculations still suggested the VW could go approximately 100 miles farther on a fill-up than the Lexus (442 versus 542 miles-the longest range of the group).

The caveat is fluctuating fuel prices. At our first stop, diesel cost 20 cents more than premium unleaded. At our second stop, the prices were the same. As of this writing, this 20 cent spread is substantiated by the Department of Energy’s list of state fuel cost averages (www.eia.doe.gov). Unfortunately for diesel lovers, California’s narrow range isn’t reflected across the country. In some regions, gas stations charge between 40 cents to 80 cents less for unleaded, which could definitely be a diesel deal breaker.

At decision time, both the Mercedes-Benz and BMW seem to slip by the wayside. Though the X5 xDrive 35d delivers the best diesel fuel economy and an exhilarating drive, it also shows glaring incongruities. Those sticky Michelins that felt so grippy on the street prove useless off-road, as does BMW’s clearly street-tuned all-wheel-drive system. We managed to get our X5 stuck three times, which is three more times than either the Lexus or VW became mired. We expect more utility from a luxury SUV-especially one that costs $65,000. “Bags of fun to drive in the dry, and I really dig the motor, but the cockpit leaves me cold, the lack of off-road prowess gives me pause, and the pricetag induces heart palpitations,” says St. Antoine.

The ML320 BlueTEC performance was just the opposite; reassuringly solid, but without any memorable moments, despite such trick features as adjustable shocks and air suspension. Kiino is most charitable, but still damns it with faint praise, calling it “a nice compromise” and “perhaps the safest bet here.” Williams concurs, “Doesn’t seem to be best in any category, but a player in all.”

So the question ultimately boils down to: What do you intend to do with your SUV? If it’s spending weekdays in stop-and-go traffic and weekends roaming the urban jungle, then the value-laden Lexus may be for you. “Sure, it can’t compete in towing, off-road abilities, and cruise range, but it does everything else pretty well. Plenty fun, responsive, and capable for the soccer moms and baseball dads running around the suburbs,” says Kiino. St. Antoine agrees, “Overall, there’s a lot of tech for the money built into this rig, but it’s almost completely lacking in “SUV” feel.”

Our contention is that an SUV, whether standard or luxury grade, hybrid or diesel, should provide full measures of sport and utility. That’s why we choose the Touareg TDI.

Says St. Antoine, “It’s the only fully qualified ‘SUV’ of the four. Combine its many driving charms and beauteous appointments-it’s a compelling rig in my book.” Kiino agrees, “On-road, the Touareg continues to impress, thanks to a smooth, hushed ride and a refined diesel powerplant. For off-roaders, the VW is a real treat.” With real-world fuel economy not too far off the best in class and capabilities the others can only dream about, the Touareg TDI delivers the most with the fewest compromises. It is, as Williams succinctly puts it, “Truly, a four-season vehicle.”

1ST PLACE VOLKSWAGEN TOUAREG TDIOffers the most traditional SUV functionality of the bunch, with stellar looks and just the right combination of high-tech and off-road features.

2ND PLACE LEXUS RX 450HPerfect for the iPhone-loving city-stomper, but if long/heavy hauls and more than light off-roading figure into the equation, you’ll find it too compromised.

3RD PLACE MERCEDES-BENZ ML320 BLUETECReassuringly solid on-road and off, but there’s no spark or sizzle to the one that started this genre.

4TH PLACE BMW X5 XDRIVE 35DBest diesel mileage and clearly the driver’s choice but stratospheric cost and narrow bandwidth bar it from the podium.

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